The western boundary of Westmeath is the lower part of Lough (Lake) Ree and the River Shannon, but elsewhere the county’s limits wind through the central lowland, except at Lough Sheelin in the north. The county’s terrain is largely undulating and about 200–400 feet (60–120 metres) above sea level. In the south there are numerous long, narrow glacial ridges called eskers.

Mullingar is a principal industrial town, as is the larger Athlone. About two-fifths of the county’s residents live in towns and villages. The county is largely pastoral, and the raising of cattle is especially important. There also are limestone quarries, and textile manufacturing provides a significant source of income. The main road to Galway runs to the Shannon crossing at Athlone.

Westmeath was the north Teffia part of the ancient kingdom of Meath, Longford being south Teffia. With the Anglo-Norman conquest in the 12th century, it became part of the de Lacy earldom of Meath, but it was not intensively Anglicized. In 1241 the earldom lost its unity, and, with the deterioration of the English hold on Ireland, the western part of the earldom passed out of government control. Following the 16th-century reconquest of Ireland, Westmeath was separated from Meath in 1541 and ultimately passed into the hands of English landlords. The town of Athlone had military importance as a key to the crossing of the River Shannon. Area 710 square miles (1,840 square km). Pop. (2002) 71,858; (2011) 86,164.